[llvm] Update amdgpu_gfx functions to use s0-s3 for inreg SGPR arguments on targets using scratch instructions for stack #78226 (PR #81394)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

I believe this is correct but needs the test updates 

https://github.com/llvm/llvm-project/pull/81394